This paper introduces SLIDER, a new bipedal robot featuring knee-less legs and vertical hip sliding motion. Its non-anthropomorphic design has several advantages over the conventional anthropomorphic leg design. The lack of knees reduces the overall leg weight to only 3 kg and also reduces the moment of inertia of the leg rotation. SLIDER's ultra-lightweight legs make it suitable for agile locomotion. To test the design, we created a dynamic model of SLIDER in Gazebo and implemented a two-stage walking pattern generator, achieving a walking speed of 0.18 m/s in simulation. A physical prototype of SLIDER is currently under construction for real-world testing.